The New Covenant is a spiritual covenant sealed with the blood of Jesus (Matthew 26:28, Mark 14:24, Luke 22:20, 1 Corinthians 11:25).
Jesus Christ is the mediator of the New Covenant (Hebrews 9:15, 12:24).
The New Covenant was promised to the people of Israel in the Old Testament (Jeremiah 31:31 ff).
The New Covenant is better than the old one (Hebrews 8-9).
The New Covenant was made with Israel, with the apostles as its representatives (Matthew 26:28, see Matthew 19:28, Jeremiah 31:31, Hebrews 8:8).
The church (based on the apostles, Ephesians 2:20) of Jews and Gentiles is a participant in the New Covenant (1 Corinthians 11:25, Ephesians 3:6, Hebrews 8-9) and its servants (2 Corinthians 3:6).
The servants of the New Covenant are a spiritual, <<<royal priesthood, a nation, a people for possession, to preach the gospel (1 Peter 2:9, cf. Ezekiel 37, Rev 19-20:6).
The New Covenant announced in Jeremiah 31 is <<<pre-fulfilled>> in everyone who believes. But the complete fulfillment will happen when the Jews look at the one they pierced (prophecy of Jesus' crucifixion and atoning death in the Old Testament, Zechariah 12:10), when Christ returns in glory and God pours out his Spirit on the people (Joel 3, Romans 11:25-32, cf. Ezekiel 37, Rev 19-20:6).
<<<Behold, days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah: not like the covenant I made with their fathers on the day I took them by the hand to lead them out of the land of Egypt, this my covenant which they broke; and yet I had married them, says the Lord. But this is the covenant that I will make with the house of Israel after those days, says the LORD: I will put my law within them, and I will write it in their hearts; and I will be their God, and they shall be my people>> (Jeremiah 31:31-33).